The invention relates in general, to phonograph pickups and pickup arms and more particularly to an auxiliary device for precision adjusting phonograph pickups and pickup arms, wherein the auxiliary device is designed for placement on the turntable.
The correct mounting and adjustment of the pickup and pickup arm has fundamental importance for optimizing the function of today's high quality pickups, and for as sparing a tracking of record as possible. Upon the purchase of a new phonograph, for example, the purchaser himself, may wish to mount and adjust the pickup, even though he frequently is not skilled in this regard and does not have the proper means for adjustment. The problem is complicated by the fact that certain necessary adjustments affect others and must, therefore, alternately be repeated.
Basically, the following adjusting operations must be executed most exactly:
1. Adjustment of the overhang (the distance by which the pickup stylus overhangs the turntable spindle when a conventional arm is moved to the center of a record)
The overhang is adjusted in order to optimize the error angle during movement of the pickup arm across the record. An error angle results from the fact that the grinding axis of the stylus exactly coincides with the groove tangent only at two points of the record surface. In practice, this means that if the pickup arm is moved up to record center, the stylus is not aligned with the record center but projects or "overhangs" slightly beyond. The distance between the record center and the stylus depends among others on the shape and length of the pickup arm. Any incorrectly adjusted overhang increases distortions resulting from the error angle which can never be eliminated with conventional pickup arms. To check the correct overhang which is adjusted by shifting the pickup arm in its support, templates are employed indicating the position of the pickup at a predetermined angle of the arm.
2. Adjustment of the normal (perpendicular) position of the stylus relative to the record surface as viewed in the groove direction
This adjustment is frequently neglected. In fact however, this position affects the cross-talk attentuation between the two sound channels of the stereo record and, particularly, the wear of the record if a specially ground stylus is used. It is a common practice to check this normal position by placing a flat mirror on the turntable and observing whether the edges of the pickup housing align with their mirror images. If not, the sound head support must be turned in the pickup arm. Difficulties arise with this method in instances where due to its shape, the pickup cannot show a clear mirror image alignment, or if the thickness of the mirror does not exactly correspond to that of the record.
3. Adjustment of the pickup arm tube in horizontal position
Some pickup arms have a vertically adjustable fulcrum. This makes allowance for different heights of the pickup. Since the superelevation between the arm fulcrum and the stylus point affects the track angle, an exactly horizontal position of the arm is needed to eliminate distortions. Up to the present time, this has been done merely by optically checking the constant spacing between the pickup arm tube and the record surface.
4. Checking the vertical tracking angle
While cutting a record, the cutting stylus is inclined by 15.degree. to 20.degree. against the running direction of the cut matrix. To minimize distortions or intermodulation during the production of the record, the pickup stylus also is held in this angular position. Since the commercially available pickups may vary in size, the actual vertical track angle should also be checked, in addition to the checking of the horizontal position mentioned under 3 above, which however, cannot be done by the user without employing special instruments.
5. Adjustment of the downward pressure or stylus force
It is absolutely necessary to keep to the downward pressure in the range indicated by the pickup manufacturer in order to avoid distortions and record damages. Frequently, however, a sufficiently accurate scale is not provided on the pickup arm. Therefore, the checking can be done only with a special pickup arm balance.
Thus, it is clear that many of the necessary adjustments are only very inaccurately completed by technically unskilled persons, or that a number of additional adjusting and checking devices are needed.